Pay money to Rosatom, they'll build nuclear plants for you. If US lost its nuclear competency, it does not mean that everyone else lost.

Correct answer. Floating nuclear power plant recently went operational , supplying arctic city with electricity ; it was built in two years, top to bottom. I wonder if couple of those in the Gulf of Mexico could've secured oil refineries' energy supply, allowing grid operators to divert more conventionally generated power to residential areas, diminishing blackouts

The floating power plants from Rosatom are like 70 megawatt, a pittance vs the blackouts Texas saw. The root problem in Texas was insufficient winterization of the grid, caused by the incentives of their energy market approach. This would have still been the case even if Russia had 100 reactors floating off the Texas coast ready to hook up.

There's significant latency in oil supply chains. Weeks if not months. Keeping a refinery online does not somehow keep a power plant online or the lights on in the cities in the proximate sense. Oil refineries are irrelevant to what happened.

... Not to mention the decommissioning costs

I wouldn't be so sure about cobstruction costs either. Reactors are being built elsewhere in the world all the time, and I doubt foreign finance guys are less smart or safety codes are less strict